There is a need for highly sensitive diagnostic tools for the detection of biological analytes in the pharmaceutical, diagnostics, agriculture, veterinary and health care industries. The use of resonant light scattering as an analytical method in these areas is an emerging technology that is ripe for further development. A key component of such methods is particles or microspheres having unique resonant light scattering properties.
The use of resonant light scattering as an analytical method for determining a particle's identity and the presence and optionally, the concentration of one or more target analytes has been described (Prober et al., copending and commonly owned U.S. patent application Ser. No. 10/702,320 and U.S. Patent Application Publication No. 2005/0019842). In that method, a microparticle is irradiated with light of a given wavelength and the resonant light scattering from the microparticle is detected. As the incident wavelength is scanned (i.e., varied over an analytical wavelength range) a scattering pattern or scattering spectrum as a function of wavelength results. Each particle has a distinct resonance light scattering spectrum that can be used to identify the particle. The presence and optionally the concentration of a target analyte can be determined from the shift in the resonance light scattering spectrum that occurs when the analyte binds to a capture probe attached to the surface of the particle. The magnitude of the shift is related to the concentration of the analyte in the solution.
A key aspect of the above described method is the nature of the particle, and the ability of the particle to both bind a bio-analyte while at the same time retaining light scattering properties. The dynamic range and the sensitivity of the method are limited by the amount of bioprobe that can be attached to the surface of the particle. Modifications of the particle that could enhance the dynamic range and the sensitivity of the resonant light scattering measurements would be an advance in the art. One tool for such a modification encompasses the use of nanoparticle composite coatings for the surface modification of these particles.
The use of sol-gel materials to modify particle or nanoparticle surfaces is known (see review by Schmidt et al., Journal of Sol-Gel Science and Technology (2000), 19(1/2/3), 39-51). This technology has been applied in processes for the analysis of bio-analytes. For example, Flora et al., (Analyst (Cambridge, United Kingdom) (1999), 124(10), 1455-1462) teach the use of sol-gel particles for the adsorption of proteins for fiber-optic analysis. Similarly, glass beads comprising coatings of zirconia (Malik et al., (Indian Journal of Chemical Technology (2000), 7(2), 64-67) or alkoxysilane (Kuramoto et al, JP02097581) have been prepared and used to immobilize enzymes. Additionally, colloidal sol-gel composites have been coated on the surface of SiO2 particulate substrates to modify light transmission properties of the substrate (Garvey et al., EP246757), and non-colloidal sol-gel coatings have been applied to glass beads to modify the refractive indices of the beads (Jun et al., KR2002017667), by using the so-called sol-gel reaction. Additional modification of glass surfaces with sol-gels have been reported, see for example Carturan et al., (Journal of Non-Crystalline Solids (1984), 63(1-2), 273-81) describing coating glass beads with thin layer porous oxides comprised of SiO2/Al2O3/Na2O; and Jardine, A. Peter, (Materials Research Society Symposium Proceedings (1995), 37, (Hollow and Solid Sphere and Microspheres: Science and Technology Associated with Their Fabrication and Application), describing the synthesis of Pb(Ti,Zr)O3 (PZT) coatings on glass microspheres using sol-gel techniques; and Haraguchi et al. (Surface Science (2004), 548(1-3), 59-66), reporting the fabrication of a uniform TiO2 thin film on SiO2 microspheres.
Although the above described particle modifications are useful, none of the disclosures teach a particle having enhanced binding for bio-analytes or the compositions needed for detection by resonant light scattering means. Applicants provide herein a new glass particle having been modified with a nanoparticle composite coating that provides for greater density of bioprobe loading on the surface of the particle, resulting in enhanced dynamic range and sensitivity in resonant light scattering assays.